Process and apparatus for heating hydrocarbons

ABSTRACT

The invention covers a process and an apparatus for heating gaseous or liquid hydrocarbons within a reaction apparatus in which the hydrocarbons are cracked at high temperatures and elevated pressures. The reaction product is then fed, for example, to a high-pressure synthesis plant. The flue gas is fed to the reaction furnace at a pressure that approximates the reaction pressure on the product side.

United States Patent Mevenk-amp et a1.

[54] PROCESS AND APPARATUS FOR HEATING HYDROCARBONS [72] Inventors: Paul Mevenkamp, Lichtendorf; Hans-Dieter Marsch, Dortmund, both of Germany [73] Assignee: Friedrich Uhde GmbH,

mund, Germany [22] Filed: April 6, 1971 [21] Appl. No.: 131,795

Related US. Application Data [63] Continuation of Ser. No. 845,676, July 22,

1969, abandoned.

Dort- [52] US. Cl. ..60/39.02, 60/39.51 R, 60/39.18 C, 122/240 B, 122/356, 196/116, 165/143 [51] Int. Cl. ..Cl0g 9/20, F02c 3/24 [58] Field of Search ..60/39.02, 39.07, 39.12; 196/110,116, 117

[56] References Cited UNITED STATES PATENTS 2,035,239 3/1936 Levine ..196/117 Sept. 5, 1972 2,146,497 2/1939 Barnes 196/1 16 1,714,893 5/1929 Smith ..122/4 2,613,654 10/1952 Becker 122/240 B 2,958,189 11/1960 Britton ..60/39.71 1,714,893 5/1929 Smith ..122/4 2,439,473 4/1948 Kalitinsky ..60/26l 2,570,591 10/1951 Price ..60/261 x 2,613,654 10/1952 Becker ..122/240 B 2,958,189 11/1960 Britton et a1 ..6o/39.71 x 3,002,347 11/1961 Sprague ..60/39.18 B x 3,227,151 1/1966 Seifert ..122/240 x Primary Examiner-Douglas Hart Attorney-Malcolm W. Fraser 7] ABSTRACT The invention covers a process and an apparatus for heating gaseous or liquid hydrocarbons within a reaction apparatus in which the hydrocarbons are cracked at high temperatures and elevated pressures. The reaction product is then fed, for example, to a high-pressure synthesis plant. The flue gas is fed to the reaction furnace at a pressure that approximates the reaction pressure on the product side.

2 Claims, 2 Drawing figures V SHEEI 2 BF 2 FlG.2

INVENTORS PROCESS AND APPARATUS FOR HEATING HYDROCARBONS This application is a continuation of application Ser. No. 845,676, filed July 22, 1969, now abandoned.

BACKGROUND OF THE INVENTION Plants that include units for the production of synthesis gas and for high-pressure synthesis require considerable energy to heat the hydrocarbons in the cracking furnace and for driving compressors. In order to meet the mechanical energy requirements of such plants, it has already been suggested previously to employ gas turbines instead of steam turbines. In this case, the turbine inlet temperature is limited by producing the power gas through combustion with large excess of air. The oxygen-rich flue gases leaving the turbine are fed to the reaction furnace as combustion air, or they may be used for heat generation. Normally, the reaction furnaces are tubular furnaces whose flue gases are at near atmospheric pressure so that most of the heat transfer is by radiation. However, tubular furnaces with circulating gas heating are also known in which convective heat transfer plays a major part; here, too, the flue gases are at a pressure that is only just sufficient to overcome the flow resistance.

SUMMARY OF THE INVENTION The object of the present invention is to reduce the fuel consumption needed for heating the reaction products and for generating the mechanical driving power in a plant incorporating steps for the production of synthesis gas and for high-pressure synthesis, and to find a suitable apparatus for realizing same.

According to the invention, the problem is solved by feeding the flue gas to the reaction furnace at a pressure that approximates the reaction pressure on the product side. The elevated pressure of the flue gas flowing through the tubes or the shell space of the reaction furnace will substantially improve the heat transfer on the flue gas side, and, in addition, will relieve the pressure load on the reactor tubes which are normally subjected to heavy duty. The improved heat transfer on the flue gas side and the pressure relief on the heating tubes will result in the ability to replace the hitherto common reaction furnaces by much smaller units equipped with tubes with thinner walls.

It is well known that, in order to reduce the temperature of the flue gases coming from the combustion chamber to a level suitable for the apparatus in which it is to be applied, the combustion must take place with an increased excess of air. The disadvantage of this is, however, that a greater quantity of combustion air has to be compressed and heated and that its heat cannot be fully recovered.

With the system of firing the furnace with pressurizing gas according to this invention, the above disadvantage may be eliminated through a further invention, according to which the reaction furnace is divided into at least two units connected in series as regards the flue gas, and the burner of the second furnace unit is then fed with the flue gas from the first furnace unit whose burner is operated with an excess of air. Through the multistage heat generation according to this invention, the temperature of the flue gases and, consequently, the wall temperature of the heating tubes may be limited to a permissible value without the flue gases leaving the entire furnace arrangement having too great an excess of air.

The pressure of the flue gas roughly corresponds to that of the reaction products on the other furnace tube side. After the flue gas leaves the reaction furnace it is expanded in a gas turbine whose power output can be utilized to drive compressors of an integrated synthesis plant, to compress the combustion air, and to generate electric power.

The use of the gas turbine in conjunction with the multistage heat generation in the reaction furnace according to this invention will bring about a substantial lowering of the plant operating costs.

A further subject of the invention covers the design of a reaction furnace that is suitable for the process and which permits the thermal expansion of the thermally stressed tubing system to be controlled. For this purpose, the reaction furnace is subdivided into two furnace units arranged side by side and connected in series as regards flue gas. The product inlet and outlet openings are arranged in the vicinity of a plane serving as reference point for the furnace and the product line connecting the two furnace units is at the opposite end of the reference point, i.e. at the movable end of the furnace. The reference point is normally taken as the area immediately below or above the tube sheets of the reactor which is installed in a vessel that is insulated on the inside and under flue gas pressure. The division of the reaction furnace into at least two units is such that the product gases leave the first unit at a temperature of about 700C and, apart from CO CO, H and H 0, only contain methane and some ethane. This enables the product gases to be fed from the first to the second furnace unit in a simple pipe constructed of a normal material suitable for high temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of a typical reaction furnace according to this invention; and

FIG. 2 is a schematic illustration of an example showing the arrangement according to the invention for heating the reaction products and generating mechanical energy in gas turbines.

DESCRIPTION OF THE PREFERRED EMBODIMENT The reaction furnace, as shown in FIG. 1, is divided into two units 1 and 2 insulated on the inside with builtin reaction vessels 3 and 4, respectively. Each unit is equipped with a heating device 5 and 6. Compressed and pre-heated (e.g. 22 atm.abs. and approximately 300C) combustion air is fed via pipeline 7 to the first combustion chamber 8. The fuel is burnt in the first combustion chamber 8 with an excess of air which is so great that the permissible tube wall temperature is not exceeded when the flue gases enter the tube bundle.

In the example shown, the product is fed via the line 9 around the heating tubes in counter-current to the flue gases so that the flue gas temperature is reduced from e.g. 1,450C at the inlet to 600C at the outlet of furnace unit 1, i.e. during the passage through the heating tube bundle. The flue gas then flows via the connecting line 10 to the combustion chamber 11 of the furnace unit 2 where most of the oxygen still present in the flue gas is used up by adding further fuel. During this process, the flue gas is reheated to a temperature which roughly corresponds to that in the first combustion chamber 8.

In the furnace unit 2, the flue gas is also fed in counter current to the product flowing via the connecting line 12. Seal 13 serves to reduce the quantity not participating in the heat transfer to a negligible level. A gas-tight connection is possible if cooled expansion joints are used. The product fed in via the pipeline 9 leaves the reaction furnace via the pipeline 14. Both pipelines 9 and 14 are arranged in the vicinity of a plane serving as reference point for the reaction furnace.

As shown in FIG. 2, combustion air is sucked in from the atmosphere, compressed in two compression stages 15 and 16 with an interposed intermediate cooler 17 to e.g. 20 atm.abs. and heated in flue gas heat exchanger 18 to about 300 C. The flue gases leave the furnace 19 described with respect to FIG. 1 at a temperature of some 800C and are subsequently expanded in gas turbines 20 and 21. Gas turbine 20 drives a generator 22 and the process air compressor 23. The process air compressor compresses air which has been diverted from the combustion air via the intermediate cooler 24. Turbine 21 drives combustion air compressors l5 and 16. Before the flue gas enters the stack 25, residual heat can be extracted in a heat exchanger 26.

We claim:

1. Method of heating hydrocarbons, which consists feeding compressed and preheated gases with an excess of air to one end of a first reaction chamber, heating the gases in such chamber,

conducting the gases from the opposite end of said first reaction chamber to one end of a second reaction chamber,

heating the gases in the second reaction chamber to a temperature roughly corresponding to that of said first reaction chamber,

conducting hydrocarbons at a pressure approximately equal to the pressure inside said reaction chambers from the outside to one side of said first reaction chamber for passage through a tube bundle generally transversely of said first reaction chamber and in the path of the heated gases flowing therethrough, and

conducting hydrocarbons from the opposite side of said first reaction chamber to a second tube bundle in the second reaction chamber for passage transversely from one side to the other thereof and then to discharge and in the path of heated gases passing from one end of the second reaction chamber to the other.

2. Apparatus for heating hydrocarbons, comprising similar first and second upright furnace structures arranged side by side and separate from each other, each furnace structure having an enlarged central body portion and restricted portions on opposite ends of said body portion respectively,

means providing an air inlet adjacent the lower restricted portion of the first furnace structure,

a burner adjacent said air inlet means,

means providing a connecting duct between the upper restricted end portions of said furnace struc- Hires remote fro%said air 'nlet, thereby enabling ue gases to flow om one umace struc ure to t e other,

a burner in the region of said connecting duct and at the upper end portion of the second furnace structure,

gas outlet means for the lower restricted end portion of the second furnace structure,

tube sheets for receiving hydrocarbons and substantially filling said respective central body portions,

an inlet through the wall of the central body portion of the first furnace structure for the upper end of the respective tube sheet,

an outlet through the wall of the central body portion of the second furnace structure for the other tube sheet and disposed approximately in line with said tube sheet inlet,

means for attaching the upper ends of said tube sheets to the respective furnace structures, and

a pipe connecting the lower ends of said tube sheets. 

2. Apparatus for heating hydrocarbons, comprising similar first and second upright furnace structures arranged side by side and separate from each other, each furnace structure having an enlarged central body portion and restricted portions on opposite ends of said body portion respectively, means providing an air inlet adjacent the lower restricted portion of the first furnace structure, a burner adjacent said air inlet means, means providing a connecting duct between the upper restricted end portions of said furnace structures remote from said air inlet, thereby enabling flue gases to flow from one furnace structure to the other, a burner in the region of said connecting duct and at the upper end portion of the second furnace structure, gas outlet means for the lower restricted end portion of the second furnace structure, tube sheets for receiving hydrocarbons and substantially filling said respective central body portions, an inlet through the wall of the central body portion of the first furnace structure for the upper end of the respective tube sheet, an outlet through the wall of the central body portion of the second furnace structure for the other tube sheet and disposed approximately in line with said tube sheet inlet, means for attaching the upper ends of said tube sheets to the respective furnace structures, and a pipe connecting the lower ends of said tube sheets. 